High catalyst activity, high bulk density of a polymer and the like are important factors to be considered in a catalyst when applying it to a liquid and a gas phase polymerization. A Ziegler—Natta type catalyst comprising magnesium for polymerization and copolymerization of ethylene is known to provide high catalyst activity and a polymer of high bulk density, and to be suitable for a liquid and a gas phase polymerization, thereby having been widely used in preparation of polyethylene.
Processs for producing many titanium—based catalysts comprising magnesium for olefin polymerization have been reported. Especially, processs using a magnesium solution for obtaining a catalyst for polymerizing olefin with high bulk density have been widely known. For such examples, there have been processs for obtaining a magnesium solution by reacting a magnesium compound with an electron donor such as alcohol, amine, cyclic ether, organic carboxylic acid or the like, in the presence of a hydrocarbon solvent. Specifically, processs using an alcohol as an electron donor are disclosed in U.S. Pat. Nos. 4,330,649 and 5,106,807. Further, a process for producing a magnesium—supported catalyst by reacting such magnesium solution with a halogen—containing compound such as titanium tetrachloride is also well known in the art. Alternatively, there have been efforts to adjust the polymerization activity or molecular weight distribution of a polymer by using ester compounds in preparation of a catalyst.
However, these catalysts still need to be further improved in terms of catalyst activity, although they can provide high bulk density.
In consideration of improvement in catalyst activity, there have been U.S. Pat. Nos. 4,477,639 and 4,518,706, in which a cyclic ether, tetrahydrofuran is used as a solvent for a magnesium compound. In U.S. Pat. Nos. 4,847,227, 4,816,433, 4,829,037, 4,970,186 and 5,130,284, a catalyst for olefin polymerization which provides excellent polymerization activity and a polymer of high bulk density is disclosed, by reacting an electron donor such as magnesium alkoxide, dialkylphthalate, phthaloylchloride or the like with a titanium chloride compound. However, there still has been a need for a process for producing a catalyst for polymerization and copolymerization of ethylene which is more convenient and simpler, and can provide high catalyst activity and a polymer of high bulk density.